Application Guide - QIAxcel Advanced

112 QIAxcel Advanced Application Guide 10/2016 The strains were selected to represent all seven major E. coli serogroups and the four virulence genes. All of the samples carried the ehxA gene, which is present in most cattle fecal samples. However, the assay is only qualitative, and the ratios of the presence of the virulence genes in the table do not relate to STEC relative abundance or gene copy numbers within the cattle fecal samples. The Shiga toxin genes, especially stx2, are present in a much lower ratio in cattle samples, as described in previous publications (4, 5). QIAxcel Advanced is a high sensitivity detection platform. When dealing with samples such as cattle feces, concentration of an E. coli strain can vary significantly. With the QIAxcel ScreenGel software, weak peaks can be observed in samples containing low concentrations of E. coli strains and may be difficult to interpret (Figure 4). After analyzing several thousands of field samples, we have established the best level of confidence in data analysis by using a 5% cutoff in the QIAxcel threshold setting. This correlates best with manual interpretations. Figure 2. Electropherogram of the control sample from lane 12. All 11 amplicons used for identification are clearly visible and well separated. Peaks at 15 bp and 3000 bp correspond to alignment markers. Figure 3. Comparison of the analysis results obtained with agarose gel electrophoresis and the QIAxcel Advanced. Sample containing all 11 amplicons was used as a positive control (5). RFU x 1E0 O. keta O. O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O ket e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e a 15 bp 230 bp 523 bp 890 bp 587 bp 655 bp 296 bp 375 bp 417 bp 477 bp 168 bp 3000 bp 740 bp – hlyA – O111 – O157 – eae – O26 – stx2 – O145 – O121 – stx1 – O103 – O45 – 168 – 296 – 417 – 523 – 655 – 890 – 3000 Gene Size (bp) 740 – 587 – 477 – 375 – 230 – 15 –

Pages Overview